1. Technical Field
The present invention relates to dual band antenna feeds for combining two or more different frequency antenna feeds to connect to a single antenna.
2. Related Art
The dual band antenna feeds are usually designed by connecting two waveguide ports carrying signals over two separate frequency bands to a common waveguide structure which connects to an antenna operating over both bands. As illustrated in block diagram form in FIG. 1, a conventional antenna feed receives a first high frequency band of signals at input 2. The second lower frequency band is received at input 4. A filter 6, which may be a low pass, band pass, or band stop filter removes higher frequency components from the low frequency input 4 to prevent interference with signals from the high frequency input 2. Cavity-type filters are used as filter 6 to connect the waveguide ports to the common waveguide and avoid interference between the two frequency bands. Since a filter is a frequency sensitive device, its cost is high due to the tight tolerance and tuning requirements. A common junction 8 combines the signals from ports 2 and 4 to provide an output for an antenna 10.
The present invention provides a dual band antenna feed using an embedded waveguide structure made without requiring an added cavity-type filter. The dual band antenna feed of the present invention is made amenable to die-casting.
The dual band antenna feed in accordance with the present invention, referring to FIG. 2, includes a Ka and Ku band interface section 22. The interface section 22 has signals fed from a orthogonal mode transducer (OMT) and power combiner section 20. The output of the Ka and Ku band interface section 22 is provided to an antenna section 24.
The Ka and Ku band interface section 22, referring to FIGS. 3A-3D, includes two Ka band vertical polarization waveguide sections 31 and 32, and a single Ku band waveguide section 34 which carries both vertical and horizontal polarization Ku band signals. The opposing walls 36-37 of the Ku band waveguide 34 carrying the vertical polarization Ku band signals are transitioned to step down from an input section 40 to successively smaller dimensioned sections 41-44, and then to step back up in successively larger dimensioned sections 45-47 to an output section 48. The two Ka band sections 31-32 are fed into openings in the combined Ka/Ku band section 46, on opposite sides of the opening for the Ku band transition section 45. A slightly larger Ka/Ku band section 47 then transitions from section 46 to the output section 48. The output section 48 provides a combined Ka band vertical and Ku band horizontal and vertical signals. The output section 48 connects to the separate antenna section (24). With the Ka-band waveguides 31-32 having ports 56-57 facing the antenna port for radiation on opposite sides of the Ku-band section 45 port, sufficient isolation will be provided between the Ka and Ku band signals without requiring an additional filter.
The OMT and power combiner section 20 can have components as shown in FIGS. 4A-4D. The OMT 90 is a conventional device with separate Ku band vertical and horizontal polarization inputs 12 and 14 which combines the inputs to produce a single output carrying both the vertical and horizontal polarization Ku band signals. The power combiner has a first input (16) for receiving the Ka band vertical polarization signal, and functions to split the input into two separate signals provided in two separate Ka band vertical polarization waveguides 81-82.
The Ka and Ku band interface section 22 can be manufactured from a single block of stock metal. The stock metal block is first cut into two halves, and the Ka band waveguides are machined into the halves. The two halves are then each cut in half to form a total of four quarter sections. The Ku band waveguide is then machined into the quarter sections, and the quarter sections are reassembled to form the completed interface section 22. The quarter sections can be used to form molds which are then used for die casting to enable rapid manufacturing of multiple interface sections 22.
In one embodiment, the antenna feed can include a dielectric insert as shown in FIGS. 8A-8C. The dielectric insert includes Ka band inserts 110 and 111 which insert into Ka band sections 31 and 32 to improve matching between the Ka band sections 31 and 32 and combined Ka/Ku band section 46. A notch 114 is further included to improve the match between the Ku band section 45 and combined Ka/Ku band section 46. The insert has a rectangular portion 106 which transitions into a tapered conical section 108 which extends into the antenna portion 24 of the antenna feed.